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Chemistry

使用离子淌度-质谱对Ni（II）和Zn（II）三元配合物进行热化学研究

Published: June 08, 2022
doi:
10.3791/63722
, , , , , ,
1Department of Chemistry,Texas A&M University-Commerce, 2Laboratoire de Chimie Théorique,Sorbonne Université

Summary

本文介绍了一种使用电喷雾离子淌度质谱，半经验量子计算和能量分辨阈值碰撞诱导解离的实验方案，以测量相关三元金属配合物解离的相对热化学性。

Abstract

本文介绍了一种实验方案，使用电喷雾离子迁移率质谱（ES-IM-MS）和能量分辨阈值碰撞诱导解离（TCID）来测量带负电荷的[amb+M（II）+NTA]-三元络合物解离成两个产品通道的热化学：[amb+M（II）]+NTA或[NTA+M（II）]– + amb，其中 M = 锌或 Ni 和 NTA 是硝基三乙酸。这些配合物含有一种替代金属结合（amb）七肽，其主要结构为乙酰基-他的1-细胞 2-Gys3–亲4-泰尔5-他的6-细胞7 或乙酰-阿斯普1-细胞2-Gly 3-亲4-泰尔5-他的6-细胞7，其中氨基酸的Aa1，2，6，7 位置是潜在的金属结合位点。通过比较三元配合物及其产物的电子能量及其碰撞截面（CCS）与ES-IM-MS测量的能量和碰撞截面（CCS），从量子化学计算（目前为PM6半经验哈密顿算子）中选择了几何优化的稳态。从PM6频率计算中，三元复合物及其产物的分子参数使用竞争性TCID方法模拟两个产物通道的能量依赖性强度，以确定与解离的0 K焓（ΔH0）相关的反应的阈值能量。使用PM6旋转和振动频率的统计力学热和熵校正提供了解离的298 K焓（ΔH298）。这些方法描述了一种EI-IM-MS例程，该例程可以确定一系列三元金属离子配合物的热化学和平衡常数。

Introduction

本研究描述了一种使用市售离子淌度质谱仪的新技术，该技术允许测定替代金属结合（amb）三元金属配合物[amb + M（II）+ NTA]解离的相对热化学，其中M = Zn或Ni和NTA = 硝基三乙酸（图1）。这些反应模拟了在固定化金属亲和色谱（IMAC）1，2期间附着在NTA固定化金属上的amb标记的重组蛋白的解离。例如，使用amb A和H的amb七肽标签描述该方法（图2）（从以前的研究3，4，5，6，7，8，9，10，11，12中选择）） 具有锌（II）和Ni（II）结合特性，因此具有作为纯化标签的潜在应用。然而，所描述的过程可用于评估任何有机金属系统中的热化学能量。这些 amb 肽在 Aa1-Aa 2 和 Aa 6-Aa7 位置中具有金属结合位点，这些位点与 NTA 的羧酸盐和胺位点竞争。三个中心amb氨基酸提供间隔物（Gly3），两个臂的铰链（Pro4）和长距离π金属阳离子相互作用（Tyr5）。

[amb+M（II）+NTA]–配合物的整体1−电荷状态由其潜在结合位点的质子化状态决定。由于存在具有2+氧化态的Ni（II）或Zn（II），因此必须有三个去质子化带负电荷位点的网。[原子核+M（II）+NTA]–配合物的分子建模预测，这是两个来自NTA的质子和一个来自安布的质子（即[原子核-H+M（II）+NTA-2H]–）。产品通道包含离子物质和中性物质（即[氮氧化物-3H+甲基（II）]-+安姆或[安姆-3H+甲基（II）–+氮氧化物（3H+甲基）-+氮氧化物“）。在手稿中，“-3H”被排除在复合物的名称之外，但读者应该知道-3H是隐含的。该仪器测量两种离子质荷比（m / z）物种的相对强度。ES-IM-MS分析的一个主要属性是，它允许检查特定m / z物种的反应性，如这里和以前的amb研究3，4，5，6，7，8，9，10，11，12所使用的那样。

使用碰撞诱导的解离获取大型配合物的热化学数据是一个具有重要意义的主题13，14。包括动力学方法在内的方法不利于拟合一系列能量的数据，也不考虑多碰撞环境15，16，17，18。在这里，由阿门特劳特，欧文和罗杰斯使用引导离子束串联质谱法开发的阈值CID（TCID）方法应用于19 ，用于利用行波离子导引的新型ES-IM-MS仪器平台。TCID方法允许对三元配合物解离到其两个产物通道中的相对热化学分析，并包括一个阈值定律，该定律描述了反应物（本研究中的三元配合物）和惰性目标气体（在这种情况下为氩气）之间的碰撞能量转移。该方法包括反应物内部能量分布20上的积分，反应物和目标气体21之间的平移能量分布，以及总角动量分布22，23。解离概率和统计赖斯 -拉姆斯伯格-卡塞尔-马库斯 （RRKM） 校正由有限的时间窗口产生的动力学变化，用于观察产物24。对于两个独立的产品渠道，竞争性 TCID 方法允许同时拟合两个相互竞争的产品渠道。配合物的解离是通过轨道过渡态，它具有产物的性质，但由锁定偶极子25保持在一起。将TCID方法并入CRUNCH程序26中，并在此处描述用户界面的操作，以评估三元[amb +M（II）+NTA]– 配合物的两个解离通道的热化学性质。CRUNCH程序可根据开发人员26的要求提供。

Protocol

注： 图 1 显示了该协议的概述。 1. 试剂的制备 购买冻干的amb肽（纯度>98%）并将其储存在-80°C冰箱中。 购买纯度>99%的六水合硝酸锌（II）和硝酸镍（II）六水合物。注意：硝酸镍（II）六水合物对环境和健康有害。 购买亚硝基三乙酸、聚-DL-丙氨酸聚合物、超纯/微量金属级乙酸铵、氢氧化铵、冰醋酸和HPLC级乙腈。</…

Representative Results

竞争性碰撞诱导的 A 和 H 的 [amb+M（II）+NTA]-三元配合物解离为 [amb+M（II）]-+ NTA 或 [NTA+M（II）]– + amb，如图 3 所示。AMB 显示为 A 或 H，M = 锌或镍。[A+锌（II）+NTA]-三元配合物（图3A）表现出约0.7 eV碰撞能（CE）的明显阈值以产生[A + Zn（II）]-，以及约0.9 eV以产生[N…

Discussion

关键步骤
ES-IM-MS 阈值碰撞诱导解离 （TCID） 分析。 TCID在氩气存在下使用转移T波电池作为碰撞池。在解离之前，前体离子在通过离子迁移率（IM）电池时通过与氮气的低能碰撞而热化。这导致比使用陷阱作为碰撞池6，40所实现的更可重复的能量分辨TCID。解离前[amb+M（II）+NTA]– 的热化也允许使用298 K温度表征三元配合?…

Disclosures

The authors have nothing to disclose.

Acknowledgements

本材料基于美国国家科学基金会在1764436，NSF REU计划（CHE-1659852），NSF仪器支持（MRI-0821247），物理和天文学成功奖学金（PASS）NSF项目（1643567），韦尔奇基金会（T-0014）以及能源部（TX-W-20090427-0004-50）和L3通信的计算资源下支持的工作。作者感谢肯特·欧文（内华达大学里诺分校）和彼得·阿门特劳特（犹他大学）分享CRUNCH计划，并就PBA的安装提供建议。作者感谢加州大学圣巴巴拉分校的迈克尔·鲍尔小组分享西格玛计划。

Materials

Acetonitrile HPLC-grade Fisher Scientific (www.Fishersci.com) A998SK-4
Alternative metal binding (amb) peptides PepmicCo (www.pepmic.com) designed peptides were synthized by order
Ammonium acetate (ultrapure) VWR 97061-014
Ammonium hydroxide (trace metal grade) Fisher Scientific (www.Fishersci.com) A512-P500
Driftscope 2.1 software program Waters (www.waters.com) software analysis program
Gaussian 09 Gaussian Electronic Structure Modeling Software
GaussView Gaussian Graphical Interface to Visualize Computations
Glacial acetic acid (Optima grade) Fisher Scientific (www.Fishersci.com) A465-250
Ion-scaled Lennard-Jones (LJ) method Sigma Michael T. Bowers’ group of University of California at Santa Barbara
MassLynx 4.1 Waters (www.waters.com) software analysis program
Microcentrifuge Tubes VWR 87003-294 1.7 mL, polypropylene
Microcentrifuge Tubes VWR 87003-298 2.0 mL, polypropylene
Ni(II) nitrate hexahydrate (99% purity) Sigma-Aldrich (www.sigmaaldrich.com) A15540
Poly-DL-alanine Sigma-Aldrich (www.sigmaaldrich.com) P9003-25MG
Waters Synapt G1 HDMS Waters (www.waters.com)  quadrupole – ion mobility- time-of-flight mass spectrometer
Zn(II) nitrate hexahydrate (99%+ purity) Alfa Aesar (www.alfa.com) 12313
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Tags

Ion Mobility-mass SpectrometryTernary ComplexesThermochemistryMolecular ModelingReaction DynamicsRecombinant Protein PurificationMetal ChelationNitrilotriacetic AcidCollision-induced DissociationCollision Cross-section
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Corrales, A. J., Arredondo, A. V., Flores, A. A., Duvak, C. L., Mitchell, C. L., Spezia, R., Angel, L. A. Thermochemical Studies of Ni(II) and Zn(II) Ternary Complexes Using Ion Mobility-Mass Spectrometry. J. Vis. Exp. (184), e63722, doi:10.3791/63722 (2022).
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